Imaging the Quantum Capacitance of Strained MoS Monolayers by Electrostatic Force Microscopy.

We implemented radio frequency-assisted electrostatic force microscopy (RF-EFM) to investigate the electric field response of biaxially strained molybdenum disulfide (MoS) monolayers (MLs) in the form of mesoscopic bubbles, produced via hydrogen (H)-ion irradiation of the bulk crystal. MoS ML, a semiconducting transition metal dichalcogenide, has recently attracted significant attention due to its promising optoelectronic properties, further tunable by strain. Here, we take advantage of the RF excitation to distinguish the intrinsic quantum capacitance of the strained ML from that due to atomic scale defects, presumably sulfur vacancies or H-passivated sulfur vacancies.

Exceptional Elasticity of Microscale Constrained MoS Domes.

The outstanding mechanical performances of two-dimensional (2D) materials make them appealing for the emerging fields of flextronics and straintronics. However, their manufacturing and integration in 2D crystal-based devices rely on a thorough knowledge of their hardness, elasticity, and interface mechanics. Here, we investigate the elasticity of highly strained monolayer-thick MoS membranes, in the shape of micrometer-sized domes, by atomic force microscopy (AFM)-based nanoindentation experiments.

Quantitative magnetic force microscopy using calibration on superconducting flux quanta.

We present a new procedure that takes advantage of the magnetic flux quantization of superconducting vortices to calibrate the magnetic properties of tips for magnetic force microscopy (MFM). Indeed, a superconducting vortex, whose quantized flux is dependent upon Plank constant, speed of light and electron charge, behaves as a very well defined magnetic reference object. The proposed calibration procedure has been tested on new and worn tips and shows that the monopole point-like approximation of the probe is a reliable model.

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS.

Recent progress in the synthesis of monolayer MoS, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS grown via a refined chemical vapor deposition synthesis technique.